Phased array transmission is a wireless transmission technique that utilizes an array of antennas known as a “phased array” to reinforce the transmission of electromagnetic signals in a desired direction while suppressing them in other undesired directions. Historically, phased array transmission has been limited to military applications or other highly-specialized applications like airport surveillance, astronomy, space probe communications, and weather research. However, technological advances and lowering costs in recent years have sparked research and development efforts in more commercial and consumer-oriented areas.
As illustrated in FIG. 1, a phased array 100 generally comprises an array of antennas 102 (i.e., “radiating elements” or “radiators”) and a plurality of delay elements 104 and power amplifiers (PAs) 106 disposed in a plurality of transmission paths. The delay elements 104 are configured to delay an input radio frequency (RF) signal by different delays τ1, τ2, τ3 and τ4. The delayed RF signals are then amplified by the PAs 106 and fed to the antennas 102, which radiate the amplified and delayed RF signals into the air or space, where they spatially combine. The radiation angle 110 and transmission characteristics of the main lobe 108 of the resulting composite signal are determined by the geometrical configuration of the antennas 102 as well as the relative delays τ1, τ2, τ3 and τ4 of the delay elements 104.
The different delays τ1, τ2, τ3 and τ4 of the delay elements 104 can be implemented by simply using different lengths of transmission lines in the transmission paths between the RF input of the array 100 and the antennas 102. One limitation of that approach, however, is that the delay lines are fixed, which prevents the main lobe 108 (i.e., the “beam”) of the radiation pattern from being “steered” to different directions during operation. Various types of variable-delay delay elements have been introduced in the prior art that overcome this problem. However, they are typically notorious for having low phase accuracy, particularly when operating at high frequencies, and/or have a less than desired phase resolution, which limits the ability to precisely adjust and control the direction of transmission.